Psychiatry - Theses
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ItemHealthy Ageing in Older Veterans: A Mixed-Methods Study( 2023-10)Older military veterans are a unique population whose experiences of ageing may be different from those of their non-veteran peers in terms of physical, mental, and social health. Healthy ageing, however, has yet to be sufficiently well conceptualised for older veterans. Increased understanding of veteran healthy ageing is necessary to inform the development of health and social policy and practice that aims to support veterans to age well. This mixed-methods research aimed to extend the knowledge of healthy ageing in older veterans by exploring their perceptions of ageing well in order to examine heterogeneity in terms of their health. Study I aimed to gain an understanding of the meaning older veterans ascribed to ageing well, which was used to define health in Study II. Study II aimed to identify and examine health patterns of older veterans. Study I utilised interview data from 38 Australian veterans aged 60-75 years and reflexive thematic analysis to develop two themes, namely “Able to do what matters”, capturing autonomy, and “Caring, sharing, and being understood”, capturing connectedness. It was concluded that ageing well for the veterans in Study I meant living with expressed autonomy and sustained connectedness. Study II utilised latent profile analysis and survey data from 374 Australian veterans (M = 69.1 years; SD = 4.4) to estimate four groups with distinct health patterns. These were High Capacity (45%), Low Capacity (15%), Low Physical/High Mental Capacity (20%), and High Physical/Low Mental Capacity (20%). The health groups demonstrated a level of complexity not previously identified by past variable-level analyses. A secondary aim of Study II was to determine whether certain antecedents predicted the health patterns using multinomial logistic regression analysis. Significant predictors were educational attainment, self-efficacy, and attitudes to ageing. Specifically, higher educational attainment, greater self-efficacy, and more positive attitudes to ageing increased the likelihood of belonging to the High Capacity group compared to the other groups. The combined findings were used to develop a new framework for veteran healthy ageing, comprising a conceptual model and descriptions of four health patterns that characterise the variability in veteran health. Thus, this research developed a conceptual and empirical base for understanding veteran healthy ageing, offering future direction for expanding the evidence base in this emerging area. Findings may have practical utility for health and social policy and service provision, and implications for models of healthy ageing.
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ItemNo Preview AvailableBrain Changes in Adult-Onset Niemann-Pick Type C Disease: Neuroimaging and Other Measures( 2023-05)This thesis explores the relationship between brain changes, largely assessed through neuroimaging measures, and function in Niemann Pick type C disease. After exploring the link between psychosis and adult NPC, I set out to apply research imaging techniques I had developed and experienced during work in schizophrenia neuroimaging research to our growing adult NPC population. By first demonstrating that NPC patients showed widespread white matter as well as grey matter disease, I undertook a suite of studies that showed a significant overlap between adult NPC patients and schizophrenia patients. This group of magnetic resonance imaging-based studies largely corroborated what has been seen in animal and neuropathological studies of NPC, but hitherto had not been demonstrated in group studies in humans. I extended this work using molecular imaging to corroborate other data in neuroinflammation and tauopathy in the disease. By utilizing advanced ocular-motor analysis I further sought to find a biomarker of illness progression and treatment response. By extending this work into patients treated with a disease modifying medication, miglustat, I showed that progressive brain changes could be at least partially reversed with miglustat treatment. Lastly, my ongoing work in this area led to the development of significant expertise across neurometabolic disorders, and – by accident rather than design – allowed me to pioneer the novel psychiatric subspecialty: the psychiatry of inborn metabolic disorders.
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ItemCharacterising relationships between adolescent sleep, brain development and psychopathology( 2023-07)Background. Sleep is critical for cognitive, emotional, behavioural and physiological wellbeing, particularly during the adolescent period. Adolescents experience substantial changes in sleep behaviour, such as delays in timing, decreases in duration, changes in sleep staging and sleep-related preferences. When combined with external psychosocial demands, however, such changes often result in sleep that is chronically insufficient and of poor quality. While the relationship between poor and insufficient sleep and psychopathology is well established, little is known about the role of changes in sleep on long-term mental health outcomes. Further, little work has accounted for the comorbidity of sleep behaviours, and especially the role of comorbid sleep problems, when examining relationships between sleep and psychopathology. In addition, cross-sectional evidence suggests that relationships between sleep and psychopathology may be anchored or mediated by changes in brain structure, and substantial evidence from preclinical studies suggests insufficient and poor sleep may negatively impact the developing brain. However, little prospective work has investigated this hypothesis in humans. The general aim of this thesis was to characterise longitudinal relationships between sleep, psychopathology and brain development across adolescence. Methods. Subjective questionnaires of sleep behaviour and psychopathology, combined with structural magnetic resonance imaging data from two longitudinal studies, was used to examine prospective relationships between sleep, psychopathology and brain structure and development across adolescence. Results. In our first study, we showed that diurnal preference, a sleep-related behaviour that indexes an individual’s preferred timing of sleep, underwent non-linear delays during adolescence. This delay resulted in an overall increase in eveningness preference across the entire sample. In turn, individuals with a greater shift towards eveningness were more likely to experience externalizing psychopathology symptoms, and also evinced an attenuated trajectory of white matter development in late adolescence. In our second study, we observed substantial diversity in the types and patterns of sleep problems experienced by pre-adolescents, which further diversified in the transition into young adolescence. Changes in sleep problems over time were in turn associated with significant changes in psychopathology. In the third study, we identified associations between brain structure, insomnia and psychopathology symptoms, and that these associations showed significant overlap cross-sectionally and prospectively, indicating that similar neural regions are associated with both insomnia and psychopathology. Conclusions. This thesis demonstrates that sleep, psychopathology and brain structure and development are tightly interconnected. Sleep- and sleep-related behaviours were found to predict changes in psychopathology, and may also influence brain development and structure. Further, structural alterations associated with specific sleep behaviours are shared with psychopathology, which may indicate shared neurobiological mechanisms underpinning their established comorbidity. Taken together, findings from this thesis provide further evidence for the critical importance of sleep for adolescent mental health, and also suggest that sleep may also be important for optimal brain development.
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ItemEmotion Regulation in Post-Traumatic Stress Disorder( 2023-05)Emotion processing theory is the prevailing model which explains the development and maintenance of post-traumatic stress disorder (PTSD). While it contends that emotional engagement with the feared stimulus is paramount for recovery, emotional engagement has largely been indexed through subjective distress ratings rather than detailing the process (i.e., what is actually happening). The primary aim of this thesis is to use the Extended Process Model of Emotion Regulation to understand 1) how deficits in emotion regulation in PTSD may impair emotion processing through difficulties with emotional engagement, and 2) how these learnings could improve treatment for PTSD. To do so, this thesis builds on previous research on emotion regulation in PTSD through three papers. The first study mapped existing knowledge of emotion regulation in PTSD onto Gross’ Extended Process Model of Emotion Regulation. It identified areas in need of further research, including the integration of a more holistic model through empirical research on attitudes, beliefs, and norms in emotion regulation as well as advancing measurement techniques. These became the foundation for the second and third studies. The second paper looked at three understudied aspects of emotion regulation in PTSD: emotion perception, beliefs about emotion(s), and attitudes about emotion(s). Structural equation modelling (N=104) demonstrated that emotion perception and fixed beliefs about emotion are significantly and uniquely associated with PTSD severity, suggesting that as difficulties with the identification, clarification, and awareness of emotions and fixed beliefs about emotion increase, PTSD severity increases. Finally, the third paper used an ecological momentary assessment (EMA) design to investigate the impact of PTSD on emotion regulation strategy choice in daily life. Using data from an experience sampling study in a trauma exposed sample (N=70; 7 days; 423 observations), the results revealed that PTSD severity was linked to greater use of suppression, distraction, and rumination to manage negative emotions independent of emotional intensity. Altogether, the patterns of emotion regulation difficulties in PTSD demonstrated by this research (deficits in emotion perception, fixed beliefs about the malleability of emotions, and an overreliance on maladaptive strategies) seem to block emotional engagement thus impairing emotion processing. All in all, findings from this research suggest that emotion dysregulation is at the core of PTSD.